The general objective of this project is to study the roles of insulin and the adrenal glucocorticoids in the degradation of actin and myosin. Earlier research in the measurement of protein degradation has been hampered by the distinct possibility that these hormones might also affect the rates of amino acid accumulation, intracellular amino acid recycling and/or protein synthesis in the sensitive cells and tissues. Measurement of the efflux from muscle of 3-methyl histidine, a nonreutilizable amino acid component of actin and myosin, offers a unique opportunity to observe the effects of these hormones on the process of protein degradation without the inherent problems of amino acid uptake, amino acid recycling and protein synthesis. Methods: 1. In Vivo Experiments. - The urinary patterns of excretion of radioactively labeled 3-methyl histidine following the injection of radioactive precursors will be determined in the following groups of rats: a. normal; b. diabetic (plus or minus insulin); c. adrenalectomized (plus or minus insulin and plus or minus corticosterone). 2. In Vitro Experiments. - Perfusion of the lower extremities of the rat will provide an in vitro system in which the influences of insulin and corticosterone on the efflux of radioactively labeled 3-methyl histidine can be monitored. The same groups of rats as proposed in the in vivo experiments will be utilized in these experiments.